Washer-Disinfectors: Automated Instrument Cleaning Explained
A washer-disinfector cleans, rinses, thermally disinfects and dries instruments in one recorded cycle. How it compares with hand and ultrasonic cleaning, and what it needs to work.
Manual, ultrasonic or washer-disinfector
All three remove soil before sterilisation. They differ in consistency, in how much staff handle contaminated sharps, and in the evidence they leave behind.
| Manual cleaning | Ultrasonic cleaner | Washer-disinfector | |
|---|---|---|---|
| How it cleans | Brushing in detergent | Cavitation in a detergent bath | Spray arms or injectors with dosed detergent at set temperatures |
| Disinfects | No | No | Yes — a thermal disinfection stage |
| Rinses and dries | By hand | By hand | Automatically, in the same cycle |
| Record | Logbook only | Some units log cycles | Cycle record of times and temperatures |
| Handling of sharps | Most | Less | Least |
| Consistency | Depends on the person | Depends on loading and solution | Validated and repeatable |
Read next Manual cleaning step by stepUltrasonic cleaners in depth
Inside a typical cycle
1. Cold pre-rinse
Cool water flushes off blood and loose soil. Hot water at this stage would fix protein, so the pre-rinse is kept cool.
2. Wash
Alkaline or enzymatic detergent is dosed automatically and sprayed over — and, with injector racks, through — the instruments at the temperature that chemistry needs.
3. Neutralise and rinse
An optional neutraliser after alkaline detergents, then an intermediate rinse to remove chemical residue.
4. Thermal disinfection
A final hot rinse held at temperature — for example 90 °C for 5 minutes — usually with purified water so instruments do not spot.
5. Drying
Heated air dries the load; on machines with injector racks it is also blown through lumens.
A0: how thermal disinfection is measured
The ISO 15883 series, which covers washer-disinfectors, expresses thermal disinfection as an A0 value: the equivalent time in seconds at 80 °C, with each 10 °C above 80 °C counted as ten times more lethal. So 80 °C for 10 minutes gives A0 600, and 90 °C for 5 minutes gives A0 3000. Thermal disinfection does not replace sterilisation — critical instruments still go through the autoclave afterwards.
| A0 value | Example | Typically used for |
|---|---|---|
| 60 | 80 °C for 1 minute | Non-critical items with low contamination, such as bedpans and urine bottles |
| 600 | 80 °C for 10 minutes, or 90 °C for 1 minute | Other non-critical items that touch only intact skin |
| 3000 | 90 °C for 5 minutes, or 93 °C for about 2.5 minutes | Instruments that may carry heat-resistant viruses such as hepatitis B — the usual target for surgical and dental instruments |
Dental, clinic and CSSD machines
Dental and clinic
Countertop or under-counter single-chamber machines with racks for cassettes, trays and loose instruments, and adaptors that flush the internal channels of handpieces where the handpiece maker allows it.
Hospital CSSD
Large free-standing machines, often built into a wall as double-door pass-through units between the wash room and the packing room. Loads go in on carts, with injector racks for lumened and minimally invasive instruments; very busy departments use multi-chamber tunnel washers.
Endoscopes
Flexible endoscopes cannot take thermal disinfection. They go through dedicated endoscope washer-disinfectors that disinfect chemically, covered by ISO 15883-4.
Read next Planning a hospital CSSDDirty-to-clean room layout
Services, chemicals and daily checks
- Water: cold and hot supplies, with purified (RO or demineralised) water for the final rinse to prevent spotting; softened water helps where the supply is hard.
- Drainage and ventilation for hot water and vapour, and the electrical supply the model specifies — larger machines need three-phase power.
- Detergents, neutralisers and rinse aids from the machine maker’s approved list, dosed by pump from containers with level sensors.
- Every day: clean the chamber filters and strainer, check the spray arms turn freely and the nozzles are clear, and check chemical levels and the door seal.
- Every cycle: confirm the record shows the disinfection temperature and time were reached, then inspect instruments under magnification before packing.
- Periodically: cleaning-efficacy tests with test soils or protein residue tests, thermometric testing and revalidation under ISO 15883.
Related guides
Autoclave supply near you
Delivery, installation and training across Malaysia from Batu Caves, Kota Kinabalu and Kuching.
Frequently asked questions
What is a washer-disinfector?
What does A0 3000 mean?
Does a washer-disinfector replace the autoclave?
Do dental clinics need a washer-disinfector?
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